1. Field of the Invention
Embodiments of the invention generally relate to a splice for an optical cable. More particularly, the invention relates to a method and assembly for securing a spliced section of the optical cable.
2. Description of the Related Art
Optical sensors used in harsh environments such as within a wellbore of an oil or gas well communicate readings from within the wellbore to optical signal processing equipment located at the surface. Surface equipment transmits optical signals to the downhole optical sensors via optical cables which transmit return optical signals to an optical signal processor at the surface. The optical cables may run down the outer surface of one of the tubular strings in the wellbore such as production tubing and clamp thereto at intervals as is known in the art. Since the optical cable is exposed to the harsh effects of chemicals, high pressures, and high temperatures, the optical cables used in harsh environments typically consist of multiple layers. For example, these optical cables may have two concentric metal or alloy tubes disposed around an optical waveguide or fiber that transmits the optical signals.
A fusion splice between the ends of two fibers permits repairing a damaged section of the optical cable, coupling the optical cable to the optical sensor or surface equipment, or adding an additional length of optical cable. However, shifting of the concentric tubes or fibers therein relative to each other due to tensile loads or thermal expansion can damage the fiber that extends from the end of the optical cable. Thus, the components of the optical cable are typically secured to one another at the optical cable ends or termination points in an effort to prevent such relative movement. Further, a fusion splice creates a weak point in the fiber. A virgin fiber can accept approximately a 700,000 psi dynamic tensile load before breaking while the fiber at the splice can accept only approximately a 150,000 psi dynamic tensile load before breaking. This weakening of the fiber can effect long-term fiber reliability even under low static tensile loads. Therefore, tension on the fiber at the fusion splice must be isolated from tension forces applied to the rest of the fiber and optical cable.
A conventional method for preparing an optical cable for splicing is a complex and time consuming process. The previous method utilized roller crimping of the optical cable which could take at least an hour to prepare a single optical cable end due to the need for the operator to continually check the depth of the crimp. Even with such constant care, roller crimping subjects the process to operator variability. Further, roller crimping thins the outer coaxial tube wall making it subject to breaking and subsequent bond failure. A member crimped directly to the fiber in the previous method can cause attenuation or power loss in the fiber, especially in small (e.g. one eighth inch diameter) optical cable that has a thin buffer layer surrounding the fiber. Benefits of small diameter cable such as increased length of cable per spool, ease in handling, flexibility without kinking, and lower cost make small diameter cable preferable over larger diameter optical cable for many applications.
Therefore, there exists a need for a simplified method and assembly that secures a spliced section of any diameter optical fiber cable and fibers within the cable, preferably while eliminating or minimizing attenuation or power loss.